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Air Brake Warning and Control Devices

Air Brake Warning and Control Devices is a required knowledge area under 49 CFR 383.111(b)(1) and (b)(4). The low air pressure warning signal requirement tested here is directly codified at 49 CFR 393.51(c), which points to FMVSS No. 121 S5.1.4 (gauge) and S5.1.5 (warning signal).

Practice Air Brake Warning and Control Devices

5 Questions

  1. Federal regulation requires every air-braked commercial motor vehicle to warn the driver when air pressure drops too low to brake safely. At what point does that warning device activate?
  2. If the low air pressure warning activates while a vehicle is moving, what should the driver do?
  3. Spring brakes serve as the emergency and parking brake in an air brake system. Within what air pressure range do they begin to activate automatically as air pressure drops?
  4. In a vehicle equipped with air brakes, which control is used to set the parking brake?
  5. A tractor manufactured on or after March 1, 2001 is towing a trailer manufactured after March 1, 1998, which is required to have its own ABS. If that trailer's ABS develops a malfunction, where does federal regulation require the driver to see a warning?